The 300 PIN MSA 40 Gb TRANSPONDER protocol “REFERENCE DOCUMENT FOR 300 PIN 40 Gb TRANSPONDER” requires that a single board is capable of providing an Adaptable Power Supply (APS) with a voltage range of 1.2V˜2.5V for a 300 PIN MSA 40 Gb TRANSPONDER. The protocol gives the connection block diagram between the APS and the TRANSPONDER, as shown in FIG. 1A. According to the protocol, the pins between the APS and the 300 PIN TRANSPONDER include 4 signals which are APS Digital, APS SENSE, APS SET and GND respectively. The APS Digital is used to supply power to the TRANSPONDER, the APS SET sets the regulation point of APS output voltage and the APS SENSE signal provides remote sensing to the output voltage APS POWER. Correspondingly, there are four pins between the APS and the 300 PIN TRANSPONDER, which are APS Digital pin, APS SENSE pin, APS SET pin and GND pin respectively.
To make reckoning and understanding easy, FIG. 1A can be simplified, as shown in FIG. 1B. The calculation formula for VAPS—Digital can be obtained from FIG. 1B:VAPS—DigitalVsense×R3/(R2+R1)+Vsense  (1)
The protocol specifies the correlation between the output VAPS—Digital and resistor R1, as shown in Table 1.
TABLE 1Correlation between the output VAPS—Digital (Vout) and resistor R1R1 resistance value (Ω)Vout (V)15301.26721.53301.802.5
The Vout in Table 1 is VAPS—Digital. According to the correlation specified in Table 1 between the resistance value of R1 and VAPS—Digital, the 300 PIN 40 Gb TRANSPONDER protocol gives a parameter selection solution which can meet the correlation: Vsense=0.8V, R2=470Ω and R3=1000Ω. Based on this parameter selection solution, as shown in FIG. 1, only the power supply control chip with a reference voltage (namely, the Vfeedback in the Figure) of 0.8V can meet the requirements. This narrows the selection scope of the power supply control chip.